Electric discharge lamp



April 4, 1939 w SCOTT 2,153,009

ELECTRIC DISCHARGE LAMP Filed Aug. 28, 1956 INVENTOR WiHiam Joseph Scott Patented Apr. .4, 1939 I PATENT. OFFICE ELECTRIC DISCHARGE LAMP Williani Scott, Rugby, England, assignor to General Electric Company, a corporation of New York 7 Application August 28, 1936, Serial No. 98,380 I Great Britain September 10, 1935 l 3Claims. (01.176-126) This invention relates to electric discharge lamps and more particularly to lamps having a filling of a metal vapor and a rare gas. In such lamps at high pressure the anode and cathode functions can with advantage be fulfilled by different parts of the electrode. Good electrodes for such lamps consist of a block porous fritted metal, such as molybdenum or tungsten, impregnated with electron emitting material.

A block of porous metal however is not easily outgassed when eddy current heating is employed.

The object of this invention is to provide an improved electrode for the above type of lamp and to that end it consists in making the electrode of a coned disc preferably of porous fritted tungsten fixed or moulded around an axial tungsten wire or bundle of wires which project through the apex of the cone into the are. When out gassing an electrode of such a shape by induction heating, the larger cross-section of the cone encloses many more lines of force than a block such as hitherto used and as the walls of the disc are thin, the distance from the centre of the material to the surface is much less than in a block so that out gassing can be carried out much more easily and thoroughly. The large area of the cone is further advantageous in that during the running up period the whole of the surface may act as the anode.

The accompanying drawing illustrates this invention Fig. 1 showing one form of electrode in section secured in the end of an envelope and Fig. 2 showing an alternative form in cross section. In Fig. 1, l represents an envelope of glass or other suitable material in the end of which is mounted an electrode consisting of a cone ll of porous fritted metal such as molybdenum or tungsten impregnated with an electron emitting material. This cone II is fixed to or moulded round a tungsten wire l2 which projects through the apex of the cone. The single wire l2 may be replaced by a twisted bundle of small wires if desired. The end of the wire l2 may be made smooth or it may be enlarged by securing thereto appropriate half cycle.

operation of the lamp and provide visible light.

Alternatively the end of the tungsten wire or wires may be are welded and rounded over as shown at I 4 in Fig. 2. The disc is wholly or partly anysuitable way and may-be heat treated for instance, by firing in hydrogen before sealing it into the lamp. The axial wire I! is either sealed directly through the envelope in, or is joined to the inlead or to a heatinsulating wire loop joined to the sealed inlead, when desired. Impregnation and outgassing are facilitated by making the disc thin and by using a minimum weight of electrode material. The conical shape assures accurate centering of the are at the electrode. Athigh pressures the projecting tungsten wire or wires l3 fulfils the anode function and the outer cone surface the cathode function. At low pressures and on starting practically the whole electrode fulfils both functions thus minimizing electrode disintegration.

In order to improve the mechanical strength of the fritted mass and its adhesion to the axial wire or wires the tungsten may have a minute percentage of a metal such as nickel added to it. This can be done, for example, by adding the nickel as a powder, as a solution of one of its compounds, as a colloidal, suspension, or by ball milling the tungsten powder in a nickel container before moulding, when desired. It is important that the quantity of nickel be kept low as otherwise it is apt to evaporate and blacken the tube walls.

This addition of nickel can under certain conditions serve to improve the electrode electron emission. For starting purposes part of the inner cone surface may be covered with a layer of nickel l5 shown in Fig. 1 which is in turn coated with electron emitting material. This nickel may be a sheet or gauze washer or may be sprayed on to the tungsten.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An electrode for an electric discharge lamp device having electrodes and electrode leads sealed therein, said electrode comprising a coned disc of porous tungsten secured at its apex to a tungsten electrode lead on which said coned disc is axially mounted, the apex of said coned disc being'in closer proximity to the opposite electrode than the base thereof, said lead extending through said coned disc and projecting through the apex thereof, the end of said wire forming a rounded projection.

2. An electrode for an electric discharge lamp device having electrodes and electrode leads sealed therein, said electrode comprising a coned disc of porous, fritted tungsten having an admixture of nickel therein and a material of high electron emissivity characteristics associated therewith,

said coned disc and projecting through the apex thereof,

3. An electrode for an electric discharge lamp device having electrodes and electrode leads sealed therein, said electrode comprising a coned disc oi.

porous, fritted tungsten having an admixture of nickel therein and being secured at its apex to an electrode lead, the apex of said coned disc being in closer proximity to the opposite electrode than the base thereof, said lead extending through said coned disc and projecting through the apex thereof.

WILLIAM J. SCO'II. 

